docs: add instrumentation naming convention to contributing guide

[krrishapatel]

Description

Adds a note to the instrumentation guidelines section of CONTRIBUTING.md documenting that instrumentations should use their top-level package name (e.g. "opentelemetry.instrumentation.requests") as a fixed string when obtaining a tracer or meter, rather than __name__.

Fixes #910

Type of change

• This change requires a documentation update

How Has This Been Tested?

Documentation-only change.

Does This PR Require a Core Repo Change?

• No.

Assisted-by: Claude Opus 4.6

[xrmx]

This contains unrelated changes

[krrishapatel]

@xrmx Rebased to remove the unrelated change — this now only touches CONTRIBUTING.md. Mind taking another look?

[github-actions]

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[krrishapatel]

Closing this myself — the guidance as written is wrong, and I should have checked it against the codebase before proposing it.

I went back through the shipped instrumentations, and 35 of them pass __name__ to get_tracer, including requests, django, and flask. So this PR was telling new contributors to avoid the convention that the repo overwhelmingly follows.

The reason __name__ is correct there is that these calls live in the package's top-level __init__.py, where __name__ already evaluates to the canonical name, e.g. in opentelemetry-instrumentation-requests/src/opentelemetry/instrumentation/requests/__init__.py it is exactly "opentelemetry.instrumentation.requests". There is nothing to fix in that case.

The narrower thing I was actually reacting to is real but rare: when get_tracer is called from a submodule, __name__ picks up the submodule path instead of the package name. There are two such spots in shipped code:

• opentelemetry-instrumentation-pika/src/opentelemetry/instrumentation/pika/pika_instrumentor.py:202
• opentelemetry-instrumentation-aiohttp-server/src/opentelemetry/instrumentation/aiohttp_server/__init__.py:434 (this one is in an __init__.py, so it is fine)

That is a two-line observation about one package, not a contributing-guide checklist item, so it does not justify this PR. If maintainers think the pika case is worth normalizing I am happy to open a small targeted PR for it, but I would rather ask first than add another unsolicited one.

Apologies for the noise on this and on #4753. @xrmx your "unrelated changes" review was the correct call on the original version, and I should have validated the underlying claim rather than just trimming the diff.